THE BUILDINGS of Lars Sonck, a Finnish architect born in 1870, are today so little appreciated outside of his native land that when the august authors of a standard architectural reference book wrote their entry on Finland they misspelled his name. Lars Spronck, they called him.

Sonck's undeserved obscurity is understandable. He was perhaps the most Finnish of Finnish architects. Unlike his countryman Eliel Saarinen, who was born just three years later, Sonck stayed home. And unlike Saarinen, Sonck in his later years produced nothing of a distinction to parallel Saarinen's elegant ensemble at the Cranbrook Academy in Bloomfield Hills, Mich., designed and built in the years after Saarinen emigrated to the United States in 1923. Nor did he build the sort of influential following Saarinen did through his Cranbrook educational program.

Then, too, when Finnish architecture is mentioned everybody thinks first of Alvar Aalto. Sonck was not a world-class genius like Aalto (who was born a generation later and whose modernism definitely stole the thunder from Sonck and his generation). But Sonck was enormously skilled, as can be seen many times in an exhibition devoted to his work, currently on view at the American Institute of Architects headquarters.

Sonck's best buildings, which predate World War I, show the stamp of a powerful artistic personality. They are strong, solid, ingeniously massed, robustly textured and often beautifully detailed. The force of these buildings when they were new prompted a Swedish writer to comment that Sonck "has primeval strength, which no one else in the Scandinavian countries can rival."

For the most part, Sonck spent his early years designing villas for wooded slopes alongside the sea or beside Finland's many lakes. These massive, straightforward houses, made largely of hewed logs, look backward to early Finnish buildings. They are an important chapter in the story of the national Romantic revival that swept through all of the arts in Finland and the other Scandinavian countries toward the end of the 19th century. One of these houses, designed for composer Jean Sibelius at a time of Russian oppression, was to become something of a monument of the national movement.

When he was 23 and still a student, Sonck won a design competition for a church in Turku, a neo-Gothic design that with its high off-center tower already showed signs of the ruggedly romantic profiles chracteristic of many of his later, large buildings. St. John's Cathedral in Tampere, designed in 1903-1904, a decade after the Turku church, shows Sonck at his best. The building is notable for its complex native stonework and its vigorous fac,ades, each powerfully punctuated by different window systems and massive projecting forms.

Sonck's work of that period has been compared to the achievement of H.H. Richardson and, indeed, the work of the American architect, well-known through most of Europe at the time, may have exerted a benign influence. But the cathedral and Sonck's other major projects of the time, such as the Helsinki Telephone Company and the Eira Hospital (both 1905), are indelibly Sonck's buildings. Later buildings, such as the Helsinki Stock Exchange (1911), are similarly stamped by his strong architectural character while taking an honorable regional place in the broad stream of European Art Nouveau architecture.

After World War I, Sonck's output declined in quality, if not in quantity. As always, the process of artistic decline is fundamentally an enigma. Sonck, the eclectic, didn't adapt well to the new times, but he did continue to build solid Finnish log villas very nearly until he died in 1956. Sonck's tremendous pieces from before the war certainly deserve the belated honor of this exhibition, which was sponsored by the Embassy of Finland as part of its nationwide "Scandinavia Today" presentation.

The exhibition remains in Washington through Feb. 25. The AIA headquarters, 1735 New York Ave. NW, is open weekdays from 9 to 5.